HTTPfy

Port 4045 (npp)

IANA assigns port 4045 to npp: Network Paging Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
npp TCP Network Paging Protocol - -
npp UDP Network Paging Protocol - -

Check what is listening on port 4045

Linux: is anything listening on TCP 4045?
sudo ss -tlnp 'sport = :4045'
Linux: UDP 4045
sudo ss -ulnp 'sport = :4045'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4045
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4045 '
Windows (Command Prompt)
netstat -ano | findstr :4045
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4045 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4045
From Windows
Test-NetConnection HOST -Port 4045
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4045

Block port 4045 in the firewall

ufw
sudo ufw deny 4045/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4045 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4045 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4045' -Direction Inbound -Protocol TCP -LocalPort 4045 -Action Block
ufw
sudo ufw deny 4045/udp
iptables
sudo iptables -A INPUT -p udp --dport 4045 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4045 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4045' -Direction Inbound -Protocol UDP -LocalPort 4045 -Action Block

Related ports

92npp4043nirp4044ltp4046acp-proto4047ctp-state

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.